Page 48 - Energize June 2022

TECHNICAL

MV switchgear testing and

monitoring

Major users of electricity are dependent on the reliability and availability of medium voltage (MV)

switchgear to distribute and supply electricity to customers or plant without interruption, and to
protect the network in case of faults. MV switchgear failure can be catastrophic, causing danger
to life, service delivery interruption and loss of income. Continuously monitoring the health of
switchgear, by regular testing, can avoid catastrophic failure.

BY MIKE RYCROFT, ENERGIZE

witchgear testing technology has evolved to the point where there is a wide range the energy for the opening and the
of advanced test and analysis equipment available, for both testing and permanent closing operation to be stored. To release
Smonitoring of switchgear. Systems range from off-line physical testing only, to on-line the energy stored in the springs, two
continuous performance monitoring. coils are needed to control the springs
MV switchgear comprises several types, including air insulated, gas insulated and solid remotely. The opening spring is charged
insulation types, and although the most common failure modes differ for each type, there is during the closing operation of the
a common trend of failure modes. Typical switchgear comprises disconnectors, isolators and breaker and the closing spring is charged
circuit breakers. Circuit breakers also function as disconnectors under operator control, and by a motor.
most circuit breaker assemblies incorporate isolators and earth switches (Figure 1). Most test
procedures focus on the various circuit breaker assemblies. Switchgear failure
Modern MV switchgear types make wide use of vacuum breakers. Essential elements of Several studies conducted over the past
a switch include the interrupter unit, the mechanical linkage, and the operating mechanism few decades have identified the following
with an energy storage system. The energy needed to operate a circuit breaker is high, and main areas of switchgear failure :
2
it must be made available within a few milliseconds, i.e., almost instantaneously. Springs • Loose connections
are used in most cases because they are simple and reliable. Two separate springs allow • Insulation breakdown
• Moisture intrusion
• Failure to perform operation (open or
close)
• Loss of electrical connections (primary
or secondary)
• Dielectric breakdown
• Loss of mechanical integrity.

Switchgear which has not been operated
for a considerable time may also develop
conditions which affect operation, such as
the drying out of lubricant, etc.

Switchgear testing
Switchgear testing comprises a set
of measurements and observations,
performed on the switch to determine
the state of health of the switch. Testing
may be performed offline, online, or by
means of permanent monitoring and
recording equipment. Offline and online
testing require specifically designed
Figure 1: Switchgear layout (Megger) portable test sets.

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